Prior to the present invention, lead alloy battery terminal bushings have been mass produced by die casting with good success However, porosity occurring in some of these bushings caused faults in their stem portions which may fracture as the stem is spun riveted over when the battery cover and bushing are assembled together This results in rejection of such assembled parts adding to battery costs for recycling or remanufacture. Furthermore, in some die cast bushings, gases trapped in voids or pores in the metal cause splattering, poor fusion and poor weld penetration during the inert gas welding operation generally used to join the external bushing to the cell post to form the finished terminal. Finished terminals made with cast bushings may also have blackened cable attachment towers caused by electrolyte leaching through the pores in the bushing. This terminal discoloration is objectionable since it detracts from battery appearance and purchaser acceptance.
In addition to die cast bushings, extruded or cold formed bushings and solid terminals have been utilized or proposed prior to the present invention. For example, in U.S. Pat. No. 4,422,236 a method of extruding solid terminals for batteries is disclosed in which the terminal is formed by extrusion and a fixture of harder material is concurrently captured within the body of the terminal. In European patent application No. 0261311, a process for cold forming battery terminal bushings is disclosed in which a solid blank is pierced, cold formed and subsequently trimmed to size by removal of excess metal from opposite ends of the cold form.
The present invention relates to a process and apparatus for cold forming battery terminal bushings which advantageously utilizes substantially all of the material in a final preformed part (i.e., before cold forming) to provide a finished product that needs no trimming, cutting to size, or other finishing steps before being employed as a bushing for attachment to the battery cover and for subsequent close fitting on the battery terminal post.
The initial preform for the bushing of this invention is made from a blank of lead, lead alloy, or other suitable material by any suitable method to provide an initial shape of specified dimensions and mass. For example, the initial preform may be of a specific mass, generally torodial or donut in shape having fixed height and fixed inner and outer diameters. After the donut shaped preform is completed, it is loaded in a first of two progressive cold forming die sets stroked to make a final preform with a cylindrical stem with fixed inner and outer diameters cold worked from the donut preform. This is accomplished by a ram and forming arbor which forwardly extrudes the cylindrical stem in the die closing operation. Subsequently, in a second die set, the completely finished bushing with a flange is formed midway between the stem and a cable connecting tower for mounting the bushing to the battery cover. This tower is simultaneously formed by reversely extruding a portion of the initial preform around the arbor and within the interior of a ram that applies an axial load to the preform. The arbor further cold forms the interior wall of the bushing and a tapered central opening through the bushing is provided. During this operation, anti-turn lugs adapted to fit into recesses in the battery cover are closed die forged on the underside of the mounting flange. With this second progressive die, the formation of the bushing is complete and is properly sized so that no trimming or further operation is needed to finish the bushing. With the cold forming, the porosity of the bushing is reduced to a minimal porosity so that the stem can be readily spun riveted to form the cover and bushing assembly without breakage or damage from pore weakened metal material. In the event that single step manufacture is desired, the present invention includes compound dies which unite the principle of reverse and forward extrusion with coining in one operation. The preferred embodiments of this invention determine prerequisite dimensional limits of the bushing and include ejector mechanisms which form a part of the wall of the die cavity and which are used to remove cold formed parts axially from the dies.
It is a feature, object and advantage of this invention to provide a new and improved process of precision cold forming and finishing metallic terminal bushings for batteries and the like which eliminates the finishing of the part after removal from the cold forming dies.
Another feature, object and advantage of this invention is to provide new and improved die constructions for making battery terminal components from metallic material which includes reverse extrusion of a portion of a preform while other portions are being coined and forwardly extruded.
These and other features, objects and advantages of this invention will be more apparent from the following detailed description and drawings in which: